1. Field of the invention
This invention relates to a woven tape for technical purposes, comprising a warp consisting of a single helically wound thread or ply yarn and a weft. The weft can include vegetable fibers and at least one synthetic strand.
2. Description of the Prior Art
In a known woven tape of that kind disclosed in German Utility Model No. 1,903,481 a synthetic strand which has been covered with spun vegetable fibers is used in the warp and in the weft. The threads may be used as single threads or as a ply yarn. The fact that vegetable fibers are spun around the synthetic strand results in the woven tape having the appearance of a tape made only of vegetable fibers, such as cotton, and it has a correspondingly strong adhesion. Owing to the synthetic core strand the tape has a higher tensile strength than a cotton ribbon. In addition, the undesired large elongation of a purely synthetic tape is compensated for by the cotton fibers covering it. It has been found that in spite of the combination of the above-mentioned properties, woven tapes having a warp consisting of ply yarns no longer fulfill the requirements of a garniture tape to be used to form cigarettes and filters in suitable production machines, particularly if the tape is to travel at a speed up to and above 600 m/min. Experiments have shown that in such applications the performance requirements such as stability at elevated temperatures, small elongation, and high tensile strength must not only be increased quantitatively but that they also change proportionately in comparison with those characteristics found at a lower running speed.
A garniture tape is also known for use in cigarette-making machines in which each warp thread consists of a large number of twisted strands made of cotton fibers and the weft threads each has a large number of twisted core strands, each of which has a multifilament synthetic core which is surrounded by a covering made of cotton fibers. That structure is adopted to ensure that the woven tape even when used at high speed in a cigarette-making machine will have a satisfactory working life and will show the best possible consistency of dimensions and a high tensile strength, minimal elongation, and satisfactory dimensional stability with the corresponding frictional properties (German Patent Publication No. 26 40 949).
It is also known that aramid fibers are used in the production of ropes, cables, tubes, belts, and the like, particularly because a relatively large number of aramid structures are available on the market for use in various applications. But such products made of aramid fibers have the disadvantage that the abrasion of fibers is relatively high so that when such fibers were used in garniture tapes the tape would be susceptible to be soiled as result of electrostatic charges (Literature relating to aramid fibers: Elias/Vohwinkel "Neue polymere Werkstoffe fur die industrielle Verwendung - Struktur, Synthese, Eigenschaften, Verarbeitung", second series, Hanser Verlag, pages 242 to 255).